GALLUP, N.M. — A surge in HIV infections on the Navajo Reservation has doctors and public health workers increasingly alarmed that the virus that causes AIDS has resurfaced with renewed intensity in this impoverished region.

A report released last month by the federal Indian Health Service found there were 47 new diagnoses of human immunodeficiency virus on the reservation in 2012, up 20 percent from 2011. Since 1999, new HIV cases among Navajo are up nearly fivefold, the report found.

“I’m scared to death,” said Dr. Jonathan Iralu, an infectious disease specialist who runs an HIV clinic in this dusty town on the edge of Navajo land, not far from the Arizona border. “The numbers show there is a dangerous rise, and the time to act is now, before it’s too late.”

As with other groups in the United States, infection rates on the reservation had leveled off and deaths dropped, with help from new treatments and outreach seeking to cut through the stigma about AIDS among tribal members.

But over the past few years, the HIV numbers on Navajo land have crept up. That increase, Iralu said, can be partly attributed to the infection being detected earlier, thanks to years of HIV education programs and more routine screening.

And though the numbers are still comparatively low — there are about 200 Navajo patients tracked by area clinics — the challenges of prevention are amplified in a place where sex is still rarely discussed publicly and infection is often hidden from loved ones.

Melvin Harrison, executive director of the Navajo AIDS Network, which provides services for tribal members with HIV, said that of the 65 people his group treats, a majority have not told family or friends.

“That’s how big the stigma is here,” he said. “They are afraid of rejection.”

The intimacy of reservation life, where a hospital receptionist might be a relative or a nurse a close friend, can be a barrier to swift treatment and prevention. Mindful of those challenges, the Indian Health Service allocated $5 million over the past three years for communities to create HIV prevention, treatment and education programs.

“HIV in Indian country is very different than the rest of the world,” said Dr. Susan V. Karol, the agency’s chief medical officer. “Our communities are very small, and that can lead to people avoiding stigma, rather than getting the care they need.”